The present invention relates to a structure of a mechanism of a magnetic recording/apparatus, for example, such as a video tape recorder (VTR), which can record or reproduce a signal on a tape-like recording medium wound on a pair of reels, and, more particularly, to a structure of a shifting device for shifting reel supports, on which a pair of reels having plural different sizes (i.e., having different reel diameters and/or different distances between the reels) or a tape cassette (referred to as merely "cassette" hereinafter) including reels therein can be mounted.
In the past, as examples of such structures of the shifting device, structures using cassettes, particularly, structures applicable to two kinds of cassettes having different sizes and structures applicable to three kinds of cassettes having different sizes have been proposed. Among them, in the structure applicable to two kinds of cassettes having different sizes, generally, reel support bases, on which reel supports are mounted, abut against supporting blocks for supporting guide members such as rails for guiding the reel support bases and are maintained in a predetermined position on the supporting blocks by means of bias springs.
On the other hand, as the structure applicable to three kinds of cassettes having different sizes, a structure is disclosed in the Japanese Patent Unexamined Publication No. 62-92154. According to this structure, in order to permit the use of three kinds of cassettes having different sizes, in addition to a driving source for shifting the reel support bases along the guides and a transmission mechanism for transmitting the driving force from the driving source to the reel support bases, it is necessary to provide a positioning mechanism for positioning and holding the reel support bases in a predetermined position after the reel support bases are shifted corresponding to the cassette having an intermediate size, and a driving force generating means for operating such positioning mechanism. To this end, in this conventional structure, a motor is used as the driving source for shifting the reel support bases and the driving force generating means for operating the positioning mechanism, and a belt-pulley arrangement or a gear train is used as the transmission mechanisms therefor. Further, the combination of pin, V-shaped notch and spring is used as the positioning mechanism. In many cases, the V-shaped notches are formed in the side surfaces of the reel support bases. When the V-shaped notch moved together with each reel support base reaches a predetermined position, the pin automatically enters into the V-shaped notch, thus positioning and holding each reel support base in the predetermined position. The spring is arranged between each reel support base and the base shifting mechanism to cause the V-shaped notch of the reel support base to abut against a fixed part including the pin by a spring force thereof, thereby positioning and holding the associated reel support base at that position. By providing a sensor, after each reel support base is shifted to the predetermined position, the motor is deenergized to hold the base stationary at that position. More particularly, the sensor detects the position of each reel support base during the movement thereof and emits a detection signal, by which a control circuit is activated to shut off the supply of electric power to the motor, thus stopping the motor.
As for means for changing over the driving force transmission mechanism corresponding to the sizes of three kinds of cassettes, the combination of a control member and a plunger is used.
One problem with the above-mentioned conventional technique resides in the fact that, since the driving force for shifting the reel support bases and the driving force for positioning and holding the bases are obtained by the single motor through the differential mechanism, it is necessary to provide the changing-over means (including the plunger and the like) for changing the driving force from the motor between two driving forces, i.e., the driving force for shifting the reel support bases and the driving force for positioning and holding the bases. Accordingly, the number of parts constituting the apparatus is increased and the apparatus itself is more complicated.
Yet another problem with the above-mentioned conventional technique resides in the fact that, since when the motor is deenergized, the reel support bases cannot be immediately stopped accordingly due to inertia thereof, actual positions where the reel support bases are stopped will deviate or differ from desired positions. And, such positional deviation in the case where each reel support base is shifted from a position for a larger cassette to a position for an intermediate cassette will occur in the opposite direction to that when each reel support base is shifted from a position for a smaller cassette to the position for an intermediate cassette. In order to assure the positioning and holding of the bases with high accuracy, it is necessary to limit such positional deviation to a predetermined value or less. To this end, in the conventional techniques, high accuracy detectors and complicated control means must be prepared.
The above-noted problems will similarly occur in an apparatus of a so-called open-reel type without using the cassettes, as well as in the apparatus using the cassettes.